1. Field of the Invention
The present invention generally relates to a switching regulator and a semiconductor device having the same and, more particularly, to a switching regulator and a semiconductor device having the same, each having plural wiring lines electrically connected to ground potential and a protection circuit capable of preventing the occurrence of trouble when any one of the wiring lines connected to ground potential is electrically interrupted, thereby continuously applying an input voltage to the switching regulator.
2. Description of the Related Art
Conventionally, a typical semiconductor device has its plural ground terminals. For example, in a typical semiconductor device having an analog circuit and a digital circuit, both circuits being integrated in the same IC chip, the ground line of the analog circuit and the ground line of the digital circuit are electrically connected to each other not in the IC chip but outside the semiconductor device through their separate terminals to prevent superimposition of the switching noise generated in the digital circuit on the signals in the analog circuit through the ground line.
Further, when a large-scale integrated circuit including a logic circuit unit having logic gates and a buffer circuit unit having an input and an output connected to an external circuit and being capable of driving a large current is used, there is a known technique in that the logic circuit unit and the buffer circuit unit have separate ground lines and are connected to separate external power circuits to prevent malfunction of the logic circuit unit due to an increase of the ground line voltage caused by a large current flowing during the switching operation of the buffer circuit unit (see, for example, Japanese Patent Publication No. S64-1052).
FIG. 5 shows an exemplary circuit diagram of a conventional chopper-type step-up switching regulator.
In FIG. 5, a switching regulator 100 includes a control semiconductor device 101, an inductor L101, a rectifying diode D101, an output capacitor C101, and resisters R101 and R102 for detecting output voltage.
Further, the control semiconductor device 101 includes a switching transistor M101 constituted of an NMOS transistor and a control circuit 102 generating and outputting a control voltage Vg to turn ON/OFF the switching transistor M101. The control semiconductor device 101 further includes a power terminal Vdd, an inductor connecting terminal Lx, a feedback terminal FB inputting a voltage proportional to the output voltage of the switching regulator, a first ground terminal GND1 of the control circuit 102, and a second ground terminal GND2 of the switching transistor M101.
When the switching transistor M101 performs a switching operation, a large current flows to the ground line, and the voltage of the ground line fluctuates. Because of this feature, to prevent the degradation of the accuracy of an analog circuit operation in the control circuit 102 and the malfunction of the digital circuit, a ground terminal is divided into the first ground terminal GND1 and the second ground terminal GND2 and both terminals are connected to each other through a wiring line on, for example, a printed circuit board on which is mounted the control semiconductor device 101.
However, when the control semiconductor device 101 and its peripheral parts are mounted on, for example, a printed circuit board, if the first ground terminal GND1 is not connected to ground potential GND due to a poor connection, and a voltage is applied to the input terminal IN of the switching regulator 100, the control circuit 102 may not operate due to the disconnection between the first ground terminal GND1 and ground potential GND and the control voltage Vg output from the control circuit 102 may be increased. Further, when the control voltage Vg exceeds the gate threshold voltage of the switching transistor M101, the switching transistor M101 is disadvantageously turned ON to be electrically conducting.
As shown in FIG. 5, the inductor L101 and the switching transistor M101 are connected in series between the input terminal IN and ground potential GND of the printed circuit board. Further, since a large current flows through the switching transistor M101, the on-resistance of the switching transistor M101 is typically very low. Also, the DC resistance of the inductor L101 is low. Therefore, when the switching transistor M101 is turned ON, a large current continuously flows from the input terminal IN through the inductor L101 and the switching transistor M101. Unfortunately, as a result, a battery supplying power to the input terminal IN may be discharged and the inductor L101 and the switching transistor M101 may be overheated. Further, when this condition is prolonged, something may go wrong with the inductor L101 and the switching transistor M101.